The present invention relates to a method for forming a projection screen or a projection volume. The invention also relates to a device for implementing the aforementioned method.
In this context, a projection screen refers generally to a substantially two-dimensional surface with such light reflection and/or light scattering properties that a moving or still image, or other performances or effects based on the use of light, can be reflected on the surface by means of a projector, light effect device, laser device, or the like. In a corresponding manner, a projection volume refers to a substantially three-dimensional object that can be illuminated in a suitable manner to produce three-dimensional patters.
The most commonly used projection screens are manufactured of fabric, painted wood, metal, plastic, or other solid material. A well-known example of such a solid projection screen is the movie screen.
However, using the above-mentioned projection screens involves certain limitations. For example, in different outdoor or indoor performances, large, temporary projection screens are needed, which must be assembled and disassembled fast. In certain situations, assembling and disassembling the projection screens must be carried out also during an actual performance. The prior art recognizes various non-solid projection screens that enable more versatile uses compared to traditional solid projection screens.
U.S. patent publications U.S. Pat. No. 5,067,653, U.S. Pat. No. 5,270,752, U.S. Pat. No. 5,989,128 U.S. Pat. No. 6,092,900, German patent publications DE 476372 and DE 3130638, Swiss patent publication CH 647605, British patent publication GB 2220278, and French patent publication FR 2773229 describe various projection screens formed typically of fog. They generally describe spraying of fog or steam condensating into fog, or gas planarly from nozzles, wherein images, or the like, can be projected on the thereby generated planar fog surface either from the front of the projection screen or from the back of the projection screen relative to the observer.
A problem involved in these projection screens composed of fog, or the like, is their tendency to disperse, i.e., the planar quality of the projection screen deteriorates as the distance grows to the nozzles used in forming the projection screen. This is due to the friction caused by a fog flow of the surrounding still air and to the turbulence produced on the surface of the flow formed by the projection screen as a result of this. Obviously, as the planar quality of the projection screen deteriorates, the Image quality deteriorates respectively.
This problem is subject to discussion particularly in the aforementioned patents U.S. Pat. No. 5,067,653 and U.S. Pat. No. 5,270,752. In said patents, both sides of the projection screen are provided with air curtains, i.e. air flows that are parallel with the flow formed by the projection screen, wherein the task of these air curtains is to limit the fog flow between the air curtains as planar as possible.
Japanese patent publication JP7056235 introduces a different kind of solution for maintaining the planar quality of the projection screen. In the solution introduced in said patent publication the projection screen is formed by blowing fog or smoke from the nozzles in a manner that the resulting flow is initially laminar. To keep the flow better in shape, a separate suction apparatus is arranged on the opposite side relative to the nozzles to suck the flow forming the projection screen. An aim of this arrangement is to prevent dispersion of the flow caused by the projection screen on the stretch between the blow apparatuses and suction apparatuses.
However, in the aforementioned prior art solutions a significantly more complicated apparatus structure is needed in forming the projection screen, among other things, because separate air curtains are formed. Nevertheless, in spite of the air curtains and/or the separate suction apparatus, in practice the projection screen always disperses to some extent, thereby deteriorating the image quality. The projection screen tends to disperse more, the further away the distance to the nozzles grows. The larger projection screen is aimed to be produced, the more difficult it becomes also technically to obtain a planar projection screen.
Moreover, prior art methods are ill suited for producing other kind than merely planar projection screens. For example, steeply curved cylindrical projection screens are difficult to form. Prior art solutions are still mainly restricted to using fog (water) or smoke in forming the projection screen. Prior art is also unable to provide functional solutions for obtaining, in a satisfactory manner, projection volumes and three-dimensional patterns projected on them.
The main purpose of the present invention is to provide a novel method for forming a non-solid projection screen or projection volume in a manner that the problems present in the above-described prior art solutions can be reduced or totally prevented.
To attain this purpose, the present invention provides a method as described herein.
It is also an aim of the invention to provide a device implementing the aforementioned method.
The gist of the invention is to use a non-turbulent, i.e., laminar transfer flow that is composed of gas or liquid and is larger than the actual projection screen or projection volume, for moving the scattering centres forming the projection screen or projection volume. In accordance with the invention, the scattering centres are supplied inside said laminar transfer flow in a manner that the scattering centres move along with the flow in the central or inner part of the flow that remains laminar, without drifting to the vicinity of the interface between the transfer flow and the thereof surrounding area, there being always some flow-dispersing turbulence present in said interface. Since the turbulence occurring on the interface of the transfer flow does not reach the central or inner parts of said transfer flow to a significant degree, the flow conditions in the central or inner parts keep their laminar nature extremely well, wherein the flow of the scattering centres forming the projection screen or projection volume remains well in shape.
Because the transfer flow now contains in itself the scattering centres necessary for forming the projection screen or projection volume, separate air curtains, or the like, used in prior art methods are not required at all. Instead of the three flows (two air curtains and an actual flow forming the projection screen between these two) used typically in solutions of prior art, in the solution according to the invention only one flow containing the projection screen in, Itself is required.
As the transfer flow is composed mainly of gas, advantageously of air, the scattering centres can be, for example, aerosol particles in fluid or solid form, such as smoke, or steam. Certain gas molecules or atoms can also operate as scattering centres.
As the transfer flow is mainly composed of transparent fluid, for example water, the scattering centres can be, besides small particles of solid material, also such larger particles that can move along the fluid flow that carries them. Fluids or gas bubbles that are insoluble to the fluid of the transfer flow can also still operate as the scattering centres.
In one embodiment of the invention the scattering centres used are elastically light-scattering scattering centres, such as aerosol particles contained in smoke or fog, for example, or particles of solid material contained in fluid, or gas bubbles. In this case, the wavelength of the light scattered/reflected by the scattering centres is the same as the wavelength of the light that Illuminates them. Thus, the scattering process can be based, for example, on so-called Mie scattering, which refers to elastic light scattering that is generated from scattering centres that are larger in size relative to the wavelength of light. An advantage of this embodiment is that the projected image is easy to form in multi-colour, using conventional movie or video projectors, or the like.
In another embodiment of the invention, material is used that scatters light in a non-elastic manner, such as phosphorescent or fluorescent particles, molecules or atoms. Hence, the scattering centres are made to emit visible light by illuminating and activating them with suitable radiation having higher energy level, ie., radiation with shorter wave-length. A benefit with this embodiment is that since the light of a certain wavelength directed to the projection screen or projection volume, for example ultraviolet light that is invisible to the human eye, activates visible only certain defined areas in the target, this method can be used for forming images or three-dimensional patterns that seem to be floating in the air. Other areas of the projection screen or projection volume can be arranged, using suitable scattering centres, for example gas molecules, as scattering centres, to be substantially totally transparent in the prevailing surrounding normal light, i.e., invisible to the observer.
The solution of the invention enables forming of projection screens or projection volumes of scattering centres moving along a gas or fluid flow, the benefit of said projection screens or projection volumes being, among other things, that they take a thin and cohesive form and therefore show good image quality, that the apparatus required to form them is simple, light-weight and easy to move and use, that the projection screen and projection volume is very fast to form and disassemble, and that also other types of projection screens than planar ones can be formed.
The solution of the invention allows, while using, e.g., air for forming the transfer flow and so-called dry fog as the scattering centres, it is possible to create also walk-through projection screens and projection volumes useful for example in forming so-called virtual spaces and rooms (Projection-Based Virtual Environment, Cave Automatic Virtual Environment). The projection screen constructions of prior art virtual spaces are very expensive and difficult to form, assemble and amend. The method according to the invention is suitable also for creating various three-dimensional patterns, for three-dimensional visualisation, for producing special effects and/or staging in different indoor or outdoor scenes, or the like.